Anisotropic Conductive Films (ACF) are commonly used in flat panel display driver integrated circuit (IC) bonding. A typical ACF bonding process comprises a first step in which the ACF is attached onto the electrodes of the panel glass; a second step in which the driver IC bonding pads are aligned with the panel electrodes; and a third step in which pressure and heat are applied to the bonding pads to melt and cure the ACF. The conductive particles of the ACF provide anisotropic electrical conductivity between the panel electrodes and the driver IC. ACF has also been used widely in applications such as flip chip bonding and photovoltaic module assembly.
U.S. Published Application 2010/0101700 to Liang et al. (“Liang '700”) discloses a technique which overcomes some of the shortcomings of ACF having randomly dispersed conductive particles. Liang discloses that conductive particles are arranged in pre-determined array patterns in fixed-array ACF (FACF). Such a non-random array of conductive particles is capable of ultra fine pitch bonding without the same likelihood of a short circuit. In contrast, the conductive particles of fixed array ACFs are pre-arranged on the adhesive surface and have shown a significantly higher particle capture rate with a lower particle concentration than traditional ACFs. Since the conductive particles are typically high cost, narrowly dispersed Au particles with a polymer core, fixed array ACFs provide a significantly lower cost solution with a superior performance as compared to the traditional ones.
U.S. application Ser. No. 13/233,360 (recently allowed) discloses a process for manufacturing an ACF using a continuous belt or loop having an array of microcavities carrying conductive particles formed in one surface as the carrier web. The belt is used in a manner analogous to the web in the process disclosed in Liang '700. The belt is formed by abutting the end surfaces of a web and securing them with an adhesive such as pressure sensitive adhesive and UV or thermally curable adhesive. The abutted ends of the carrier web form a stitching line that may be at an oblique angle, i.e., less than 90° (as measured with respect to the longitudinal edges of the web). One problem with manufacturing an ACF using a continuous belt having a stitching line is that few, if any, conductive particles can be carried on the belt in the area of the stitching line because the microcavities are filled with adhesive in the area of the stitching line. In order to minimize the frequency with which an electrode (for example, an electrode in a device such as a microchip) oriented parallel the cross-machine direction of the ACF does not contact a sufficient number of conductive particles to complete a circuit the stitching line may be oriented at an oblique angle.